Composite electroless plating

ABSTRACT

This invention is a process for electrolessly metallizing an article to provide on the surface thereof a metal coating incorporating therein particulate matter, in which the process comprises contacting the surface of said article with an electroless metallizing bath essentially free of heavy metals, an electroless metallizing bath used in the process, and articles with coatings resulting from the process.

BACKGROUND OF THE INVENTION

The present invention relates in general to composite electrolessplating, and more particularly, to a process of composite electrolessplating without the intentional introduction of heavy metals, articlesresulting from the process, and plating baths used in the process.

The electroless plating of articles or substrates with a compositecoating containing finely dispersed particulate matter is welldocumented.

Electroless plating generally involves the deposition of metal alloys bychemical or electrochemical reduction of aqueous metal ions. Throughsuch deposition, the process of electrolessly metallizing a desiredmetal coating over an article or substrate is achieved.

The fundamentals of composite electroless plating are documented in atext entitled “Electroless Plating Fundamentals and Applications,”edited by G. Mallory and J. B. Hajdu, Chapter 11, published by AmericanElectroplaters and Surface Finishers Society (1990), which is hereinincorporated by reference.

As opposed to conventional electroless plating methods, in compositeelectroless plating, insoluble or sparingly soluble particulate matteris intentionally introduced into a bath solution for subsequentco-deposition onto a substrate or article as a coating.

The evolution of composite electroless plating dates back to U.S. Pat.No. 3,644,183 (Oderkerken), in which a structure of compositeelectroless plating with finely divided aluminum oxide was interposedbetween electrodeposited layers to improve the corrosion resistance.Thereafter, U.S. Pat. Nos. 3,617,363 and 3,753,667 (Metzger et al.)extended the Oderkerken work to a great variety of particles andmiscellaneous electroless plating baths. Thereafter, Christini et al.,in Reissue Pat. 33,767, further extended the composite electrolessplating technique to include the co-deposition of diamond particles. Allof the foregoing references are herein incorporated by reference.

The co-deposition of particles in composite electroless plating candramatically enhance existing characteristics and even add entirely newproperties. These capabilities have made composite electroless coatingsadvantageous for a variety of reasons including, but not limited to,increased utility in conditions requiring less wear and lower friction;facilitating the use of new substrate materials such as titanium,aluminum, lower cost steel alloys, ceramics, and plastics; allowinghigher productivity of equipment with greater speeds, less wear, andless maintenance related downtime; and replacing environmentallyproblematic coatings such as electroplated chromium. In this lastregards, for example, composite electroless coatings with nickel evenprovide an additional environmental advantage over conventionalelectroless nickel coatings, which do not include particulate matter, inthat the particles within composite electroless nickel coatings reducethe amount of nickel alloy used. Specifically, composite electrolessnickel plating reduces the amount of nickel introduced to theenvironment by a percent equal to the volume percent of the particulatematter within the composite electroless nickel coating.

In addition, composite electroless coatings are regenerative, meaningthat their properties are maintained even as portions of the coating areremoved during use. This feature results from the uniform manner withwhich the particles are dispersed throughout the entire plated layer.

However, known composite electroless plating processes suffer from anumber of disadvantages. In particular, composite electroless platingbaths, in general, are inherently unstable and prone to decomposition.To overcome this instability, the standard approach is the use of heavymetals in the plating baths. This incorporation of heavy metals into theplating baths presents multiple challenges. The heavy metals must beadded in a sufficient amount to prevent the decomposition of the platingbath, but an increased concentration beyond the necessary level requiredto prevent the decomposition results in cessation or reduction of theplating rate.

Accordingly, there is still an unsolved need for further improvements incomposite electroless plating methods.

SUMMARY OF THE INVENTION

All composite electroless plating techniques known in the art, includingthe art referenced above, incorporate the intentional addition of heavymetals in the plating process. Specifically, these heavy metals, thatinclude lead, mercury, cadmium, and thallium, are utilized asstabilizers to prevent the decomposition of plating baths. However, theuse of such heavy metals has drawbacks. As explained in U.S. Pat. No.6,306,466, increased concentration of heavy metals in electrolesscomposite plating baths above a minimum level necessary forstabilization results in a diminished plating rate.

One possible reason for this substantial decrease in plating rate isthat while hydrogen bubbles emanate from the surface of all articlesbeing plated in all varieties of electroless baths, there is apropensity for such bubbles to cling to the surface of articles beingplated in certain composite electroless baths for a longer amount oftime than in a conventional electroless baths, which causes a furtherreduction of the plating rate. The accumulation of bubbles on thesurface of articles being plated in a composite electroless bathrestricts the release of depleted solution from the surface andsubsequent replenishment of fresh solution to the surface that wouldresult in renewed plating at that site.

The relatively low plating rate of certain composite electrolessprocesses has resulted in the thickness specification for many articlestreated in the processes being lower than the typical thicknessspecification for electroless processes without insoluble or sparinglysoluble particulate matter. While the frictional and release propertiesof composite electroless coatings are generally independent of thecoating's thickness, numerous other properties of the coating aredependent on the coating thickness such as wear resistance and corrosionresistance. Therefore, resorting to thinner composite electrolesscoatings inherently reduces the coating's wear and corrosion resistanceand consequently has limited the extent of applications for whichcomposite electroless coatings can be commercially utilized.

In addition, the inclusion of insoluble particulate matter in compositeelectroless baths introduces additional instability. To overcome theextra instability due to the addition of insoluble particulate matter tothe bath, as described in U.S. Pat. No. 6,306,466, the prior art teachesthe use of particulate matter stabilizers (PMS), which are believed toisolate the finely divided particulate matter, thereby maintaining its“inertness”. Also, particulate matter stabilizers tend to modify thecharge on the particulate matter to maintain its inertness. Altogether,the precise addition of particulate matter stabilizers addresses theinstability issues directly related to the addition of insolubleparticulate matter to the plating baths, as shown in U.S. Pat. Nos.4,997,686, 5,145,517, 5,300,330, 5,863,616 and 6,306,466.

However, Applicants have found that the particulate matter stabilizersalso act to prevent the decomposition of the plating baths, such thatthe intentional introduction of heavy metals is no longer necessary tostabilize the bath. In addition, although it was previously known thatan increased concentration of heavy metals above a minimum levelnecessary for stabilization resulted in a reduced plating rate,Applicants unexpectedly found that a reduction of heavy metalconcentration below a minimum level required for stabilization actuallyincreased the plating rate for many types of coatings.

Accordingly, an object of the present invention is to provide a processof composite electroless plating without the intentional introduction ofheavy metals, plating baths used in the process, and coatings forarticles resulting from the process.

In this regard, increasingly stringent rules and regulations thatrestrict or prohibit the use of heavy metals, such as the End-Of-LifeVehicle (ELV) Regulations and Restriction of Certain HazardousSubstances (RoHS), mean that the present invention has an extra addedbenefit. Since Applicants have found that particulate matter stabilizersstabilize the plating bath as well and overcome the instability fromadding insoluble or sparingly soluble particulate matter, use of thepresent invention complies with such regulations because it does awaywith the need for potentially costly and certainly environmentallyhazardous heavy metals in composite electroless plating.

In accordance with one embodiment of the present invention, there isdescribed a process of electrolessly metallizing an article to provideon its surface a metal coating containing particulate matter, in whichthe electroless metallizing bath is essentially free of heavy metals.

In accordance with another embodiment of the present invention, there isdescribed an electroless metallizing or plating bath for use in aprocess of electrolessly metallizing an article to provide on itssurface a metal coating with particulate matter, in which theelectroless metallizing or plating bath is essentially free of heavymetals.

In accordance with another embodiment of the present invention, there isdescribed an article with a coating, in which the coating contains anelectroless metal and particulate matter, and is essentially free ofheavy metals.

DETAILED DESCRIPTION

In describing the preferred embodiments of the present invention,specific terminology will be resorted to for the sake of clarity.However, the invention is not intended to be limited to the specificterms so selected, and is to be understood that each specific termincludes all technical equivalence which operate in a similar manner toaccomplish a similar purpose.

In the practice of the present invention, the electroless metallizingbath is formulated by adding together a metal salt, a reducing agent, aneffective quantity of particulate matter and a particulate matterstabilizer (PMS). The typical electroless metallizing bath also includesa bath stabilizer, usually in the form of heavy metals. However, thebath of the present invention is essentially free of such heavy metals.

The metal portion of the metal salt may be selected from suitable metalscapable of being deposited through composite electroless plating. Suchmetals include, without limitation, nickel, cobalt, copper, gold,palladium, iron, other transition metals, and mixtures thereof, and anyof the metals deposited by the autocatalytic process in Pearlstein, F.,“Modern Electroplating”, Ch. 31, 3^(rd) Ed., John Wiley & Sons, Inc.(1974), which is incorporated herein by reference. Preferably, themetals are nickel, cobalt and copper.

The salt component of the metal salt may be any salt compound that aidsand allows the dissolution of the metal portion in the bath solution.Such salts may include without limitation, sulfates, chlorides,acetates, phosphates, carbonates, sulfamates.

The reducing agents are electron donors. When reacted with the freefloating metal ions in the bath solution, the electroless reducingagents reduce the metal ions, which are electron acceptors, to metal fordeposition onto the article. The use of a reducing agent avoids the needto employ a current, as required in conventional electroplating. Commonreducing agents are sodium hypophosphate, nickel hypophosphite, sodiumborohydride, n-dimethyl borane (DMAB), n-diethylamine borane (DEAB),formaldehyde, and hydrazine.

The particulate matter may be any suitable particle that is typicallyused in composite electroless plating. Preferably, such particulatematter is insoluble or sparingly soluble within the plating solution. Itis also preferable that the particulate matter be inert andnon-catalytic with respect to the deposition process. Particulate mattersuitable for practical composite electroless plating may be fromnanometers in size up to approximately 100 microns in size. The specificpreferred size range depends on the application involved.

The particulate matter may be selected from a wide variety of distinctmatter, such as ceramics, glass, talcum, plastics, diamond(polycrystalline or monocrystalline types), graphite, oxides, silicides,carbonate, carbides, sulfides, phosphate, boride, silicates, oxylates,nitrides, fluorides of various metals, as well as metal or alloys ofboron, tantalum, stainless steel, molybdenum, vanadium, zirconium,titanium and tungsten. Without limitation, preferred specific examplesof particulate matter for use in the present invention arepolytetrafluoroethylene (PTFE), diamond, silicon carbide, boron nitride(BN), aluminum oxide, graphite fluoride, tungsten carbide, talc,molybdenum disulfide (MoS), boron carbide and graphite. The boronnitride (BN), without limitation, may be hexagonal or cubic inorientation.

As explained above, the particulate matter imparts specific propertiesto the coating to be deposited. These properties including wearresistance, modified friction, release, lubrication, phosphorescence,thermal conduction or insulation, and others, depending upon thespecific particulate matter utilized in the bath.

For example, for increased wear-resistance in the resultant coating,hard particulates, such as diamond, carbides, oxides, and ceramics, maybe included in the plating bath. Some examples of such carbides aresilicon carbide, tungsten carbide, and boron carbide. An example of suchan oxide is aluminum oxide.

For increased lubrication or reduction in friction in the resultantcoating, “lubricating particles,” such as polytetrafluoroethylene(PTFE), boron nitride (BN), talc, molybdenum disulfide (MoS), graphiteor graphite fluoride may be included in the plating bath. Theselubricating particles may embody a low coefficient of friction, drylubrication, improved release properties, and repellency of contaminantssuch as water and oil.

The particulate matter stabilizer (PMS) refers to an additive that actsto overcome the stability to the bath from addition of particulatematter to the bath. Any known PMS may be used in the compositeelectroless bath so long as its incorporation does not affect the basickinetics of the plating process. Such particulate matter stabilizers(PMS) are well-known, and include, without limitation, sodium salts ofpolymerized alkyl naphthalene sulfonic acids, disodium mono estersuccinate (anionic and nonionic groups), fluorinated alkylpolyoxyethylene ethanols, tallow trimethyl ammonium chloride, and any ofthe PMS disclosed in U.S. Pat. No. 6,306,466, which is incorporatedherein by reference.

The electroless metallizing bath is essentially free of heavy metals,which means the heavy metal concentration should be no more than 0.045parts per million (ppm) or 45 parts per billion (ppb). Preferably, theheavy metal concentration should be no more than 0.03 ppm or 30 ppb.

Typically, heavy metals are added to conventional plating baths tobrighten the resultant coating or stabilize the bath, regardless ofwhether or not the bath contained particulate matter. As shown in theart, these heavy metals stabilize the bath by preventing the bath'sdecomposition. Such heavy metals may be, without limitation, lead,mercury, cadmium, thallium, and bismuth.

The electroless metallizing bath may also contain one or more complexingagents. The complexing agent acts as a buffer to help control pH andmaintain control over the “free” metal salt ions in the solution, all ofwhich aids in sustaining a proper balance in the bath solution. Some ofthese complexing agents are, without limitation, lactic, malic,Succinic, Hydroxyacetic, acetic, ammonium compounds, citric.

The electroless metallizing bath may further contain a pH adjuster toalso help control pH levels in the bath. Suitable pH adjusters include,without limitation, carbonates, hydroxides, and acids that buffer at adesired pH range.

Once the bath has been prepared, it is ready for use in the electrolessplating process of the present invention. This generally involvescontacting the surface of an article with the electroless metallizingbath, which, as noted above, is essentially free of heavy metals.

However, the article to be coated may require preliminary preparationprior to this contact. This preparation includes the removal of surfacecontaminants.

The mechanism by which a coating is formed on an article in compositeelectroless plating is well known in the art. For example, U.S. Pat. No.4,830,889, which is incorporated herein by reference, describes theelectroless reaction mechanism. Generally, metal ions are reduced tometal by action of chemical reducing agents, which are electron donors.The metal ions are electron acceptors that react with the electrondonors. The article to be coated itself may act as a catalyst for thereaction. The reduction reaction results in the deposition of a coatingwith the metal (or electroless metal) onto the surface of the article.

The article to be coated may be any substrate or material capable ofbeing coated through composite electroless plating. Some examples ofsuch articles are components in high wear, abrasive, impact, cutting,grinding, molding, frictional, and sliding applications.

Once completed, this electroless plating process results in an articlewith a coating containing metal or metal alloy and particulate matter.Importantly, the coating is essentially free of heavy metals. For thecoating to be essentially free of heavy metals, the bath from which theplating took place should have been “essentially free” of heavy metals,as defined above. Notwithstanding, the coating should contain no morethan 0.1% by weight of heavy metals and preferably, no more than 0.01%by weight of heavy metals.

Generally, the electroless metal in the deposited coating is a metal ora metal alloy, usually in the form of a metal, a metal and phosphorous,or a metal and boron. The metal or metal alloy is derived from the metalsalt used in the bath. Examples of the metal or metal alloy are nickel,nickel-phosphorous alloy, nickel-boron alloy, cobalt, cobalt-phosphorousalloy, and copper.

Specifically, “electroless” nickel is an alloy of 88-99% nickel and thebalance with phosphorous, boron, or a few other possible elements.Electroless nickel is commonly produced in one of four alloy ranges: low(1-4% P), medium (6-8% P), or high (10-12% P) phosphorous, andelectroless nickel-boron with 0.5-3% B. Each variety of electrolessnickel thus provides properties with varying degrees of hardness,corrosion resistance, magnetism, solder-ability, brightness, internalstress, and lubricity. All varieties of electroless nickel can beapplied to numerous articles, including metals, alloys, andnonconductors.

Electroless nickel is produced by the chemical reaction of a nickel saltand a reducing agent. Typical electroless nickel baths also include oneor more complexing agents, buffers, brighteners when desirable, andvarious stabilizers to regulate the speed of metal deposition and avoiddecomposition of the solution that is inherently unstable. As previouslydiscussed, such brighteners and stabilizers have traditionally beenheavy metals added in small but specific concentrations to theelectroless nickel bath formulations. Cadmium has been the mostprevalent brightener while lead has been the most common stabilizer usedin electroless nickel baths since the inception of the technology.Diligent control of the solution's stabilizer content, pH, temperature,tank maintenance, loading, and freedom from contamination are essentialto its reliable operation. Electroless nickel baths are highly surfacearea dependent. Surface areas in contact with the bath include the tankitself, in-tank equipment, immersed substrates, and contaminants.Continuous filtration, often submicron, of the solution at a rate of atleast ten turnovers per hour is generally recommended to avoidparticulate contamination which could lead to solution decomposition orimperfections in the plated layer.

The following examples demonstrate the electroless plating process ofthe present invention, in which different particulate matter and metals(or electroless metals) are plated onto articles. In addition, theexamples show the increased plating rate for the composite electrolessplating process of present invention, in which the plating bath isessentially free of heavy metals, in comparison to conventionalcomposite electroless plating processes, in which heavy metals areintentionally introduced into the plating bath.

The plating rate (i.e., the rate at which a plated coating deposits fromthe plating bath onto the article being plated) is measured by thethickness of coating achieved per unit of time. Microns or mils per hourare common measures of plating rate. As shown in the following examples,the plating rate was not shown to decrease due to the addition ofparticulate matter to an electroless plating bath. Instead, the platingrate of electroless metallizing coatings essentially free of heavymetals shows an increase over the standard plating rate of those samecoatings containing heavy metals in some instances. At the very least,the examples show that such plating without the intentional introductionof heavy metals results in successful deposition of a coating, anindication that the plating bath was stabilized without the use of heavymetals, and a plating rate that either matched the plating rate ofplating with the intentional introduction of heavy metals or exceededit. As a reference, the “standard plating rate” in the examples refersto the plating rates for conventional composite electroless plating forthe particular coating deposited in each example, in which the bath usedincludes intentionally introduced heavy metals. For example, regarding acomposite electroless nickel/PTFE bath that includes intentionallyintroduced heavy metals, the plating rate is commonly about 10 micronsper hour.

EXAMPLE 1

Nickel-PTFE without Heavy Metals

A composite electroless nickel-PTFE bath was formulated. The bathincluded nickel salt providing a nickel metal concentration of 6 gramsper liter in the plating bath, a reducing agent of sodium hypophosphateat a concentration of 30 grams per liter, an aqueous dispersion of PTFEparticles and particulate matter stabilizers in a concentration of 3.6grams of PTFE particles per liter of plating bath, and other componentstypical of electroless nickel baths, but free of any lead or other heavymetals. The plating bath was operated at the parameters of pH 4.8-5.0,temperature of 90 degrees Celsius, and mild stirring agitation.

A steel panel measuring 2 cm by 5 cm was prepared by an immersion in ahot (180 degrees Fahrenheit) alkaline cleaning solution for 10 minutes,rinse in water, immersion in a fifty percent by volume concentration ofhydrochloric acid in water at 70 degrees Fahrenheit for 1 minute, rinsein water, and then immersion in the plating bath of the presentinvention at the parameters disclosed above. After 120 minutes ofplating in this plating bath the panel was removed from the platingbath. The coating on the panel was analyzed as follows.

A photomicrograph of a cross section of this coating at 1000-×magnification demonstrated a coating thickness of 35 microns, i.e.: 17.5microns per hour which 75% greater than the standard plating rate.Chemically dissolving the coating and weighing the PTFE incorporated inthe coating compared to the weight and volume of the entire coatingdemonstrated 24-27% of PTFE by volume in the coating.

The above bath representing the present invention was maintained at theconditions and parameters above for the subsequent plating of additionalsteel panels until the plating bath reached a total usage of 2 metalturnovers during which the properties of the coating on these additionalpanels was consistent with the initial example, thereby demonstratingthat the present invention is reproducible and commercially viable.

COMPARATIVE EXAMPLE 1

Nickel-PTFE with Heavy Metals

A composite electroless nickel-PTFE bath with intentionally introducedheavy metals was formulated. The one-liter bath, commercially known asNiSlip™ 510, sold by Surface Technology, Inc. of Trenton N.J., wasprepared according to the manufacturer's specifications. This platingbath included nickel salt providing a nickel metal concentration of 6grams per liter in the plating bath, a reducing agent of sodiumhypophosphate at a concentration of 30 grams per liter, an aqueousdispersion of PTFE particles and particulate matter stabilizers in aconcentration of 3.6 grams of PTFE particles per liter of plating bath,lead in a concentration of 1 ppm, and other components typical ofelectroless nickel baths. The plating bath was operated according to themanufacturer's prescribed parameters of pH 4.8-5.0, temperature of 88-90degrees Celsius, and mild stirring agitation.

A steel panel measuring 2 cm by 5 cm was prepared by an immersion in ahot (180 degrees Fahrenheit) alkaline cleaning solution for 10 minutes,rinse in water, immersion in a fifty percent by volume concentration ofhydrochloric acid in water at 70 degrees Fahrenheit for 1 minute, rinsein water, and then immersion in the plating bath at the parametersdisclosed above. After 120 minutes of plating in this plating bath thepanel was removed from the plating bath. The coating on the panel wasanalyzed as follows.

A photomicrograph of a cross section of this coating at 1000-×magnification demonstrated a coating thickness of 20 microns, i.e.: 10microns per hour, which is the standard plating. Chemically dissolvingthe coating and weighing the PTFE incorporated in the coating comparedto the weight and volume of the entire coating demonstrated 24-27% ofPTFE by volume in the coating. This is also a standard concentration ofPTFE for such a coating.

EXAMPLE 2

Nickel-Diamond without Heavy Metals

A composite electroless nickel-diamond bath was formulated. The bathincluded nickel salt providing a nickel metal concentration of 6 gramsper liter in the plating bath, a reducing agent of sodium hypophosphateat a concentration of 30 grams per liter, an aqueous dispersion ofdiamond particles and particulate matter stabilizers in a concentrationof 6 grams per liter, and other components typical of electroless nickelbaths, but free of any lead or other heavy metals. The plating bath wasoperated at the parameters of pH 4.8-4.9, temperature of 90 degreesCelsius, and mild stirring agitation.

A steel panel measuring 2 cm by 5 cm was prepared by an immersion in ahot (180 degrees Fahrenheit) alkaline cleaning solution for 10 minutes,rinse in water, immersion in a fifty percent by volume concentration ofhydrochloric acid in water at 70 degrees Fahrenheit for 1 minute, rinsein water, and then immersion in the plating bath of the presentinvention at the parameters disclosed above. After 60 minutes of platingin this plating bath the panel was removed from the plating bath. Thecoating on the panel was analyzed as follows.

A photograph of a cross section of this coating at 1000-× magnificationdemonstrated a coating thickness of 14-15 microns, i.e.: 14-15 micronsper hour, which is equivalent to the standard plating rate. Chemicallydissolving the coating and weighing the diamond incorporated in thecoating compared to the weight and volume of the entire coatingdemonstrated 15% of diamond by volume in the coating.

The above bath representing the present invention was maintained at theconditions and parameters above for the subsequent plating of additionalsteel panels until the plating bath reached a total usage of 2 metalturnovers during which the properties of the coating on these additionalpanels was consistent with the initial example, thereby demonstratingthat the present invention is reproducible and commercially viable.

EXAMPLE 3

Nickel-Aluminum Oxide without Heavy Metals

A composite electroless nickel-aluminum oxide bath was formulated. Thebath included nickel salt providing a nickel metal concentration of 6grams per liter in the plating bath, a reducing agent of sodiumhypophosphate at a concentration of 30 grams per liter, an aqueousdispersion of aluminum oxide particles and particulate matterstabilizers in a concentration of 3.5 grams of particles per liter, andother components typical of electroless nickel baths, but free of anylead or other heavy metals. The plating bath was operated at theparameters of pH 4.8-4.9, temperature of 90 degrees Celsius, and mildstirring agitation.

A steel panel measuring 2 cm by 5 cm was prepared by an immersion in ahot (180 degrees Fahrenheit) alkaline cleaning solution for 10 minutes,rinse in water, immersion in a fifty percent by volume concentration ofhydrochloric acid in water at 70 degrees Fahrenheit for 1 minute, rinsein water, and then immersion in the plating bath of the presentinvention at the parameters disclosed above. After 120 minutes ofplating in this plating bath the panel was removed from the platingbath. The coating on the panel was analyzed as follows.

A photomicrograph of a cross section of this coating at 1000-×magnification demonstrated a coating thickness of 40-45 microns, i.e.:20-22.5 microns per hour, which is equivalent to the standard platingrate. The photomicrograph also demonstrated a uniform dispersion ofparticles within the metal alloy matrix.

EXAMPLE 4

Nickel-Boron Nitride without Heavy Metals

A composite electroless nickel-boron nitride bath was formulated. Thebath included nickel salt providing a nickel metal concentration of 6grams per liter in the plating bath, a reducing agent of sodiumhypophosphate at a concentration of 30 grams per liter, an aqueousdispersion of boron nitride particles and particulate matter stabilizersin a concentration of 10 grams of particles per liter, and othercomponents typical of electroless nickel baths, but free of any lead orother heavy metals. The plating bath was operated at the parameters ofpH 4.8-4.9, temperature of 90 degrees Celsius, and mild stirringagitation.

A steel panel measuring 2 cm by 5 cm was prepared by an immersion in ahot (180 degrees Fahrenheit) alkaline cleaning solution for 10 minutes,rinse in water, immersion in a fifty percent by volume concentration ofhydrochloric acid in water at 70 degrees Fahrenheit for 1 minute, rinsein water, and then immersion in the plating bath of the presentinvention at the parameters disclosed above. After 120 minutes ofplating in this plating bath the panel was removed from the platingbath. The coating on the panel was analyzed as follows.

A photograph of a cross section of this coating at 1000-× magnificationdemonstrated a coating thickness of 45-50 microns, i.e.: 22.5-25 micronsper hour, which is somewhat faster than the standard plating rate. Thephotomicrograph also demonstrated a uniform dispersion of particleswithin the metal alloy matrix.

EXAMPLE 5

Nickel-Silicon Carbide without Heavy Metals

A composite electroless nickel-silicon carbide bath was formulated. Thebath included nickel salt providing a nickel metal concentration of 6grams per liter in the plating bath, a reducing agent of sodiumhypophosphate at a concentration of 30 grams per liter, an aqueousdispersion of silicon carbide particles and particulate matterstabilizers in a concentration of 3.5 grams per liter, and othercomponents typical of electroless nickel baths, but free of any lead orother heavy metals. The plating bath was operated at the parameters ofpH 4.8-4.9, temperature of 90 degrees Celsius, and mild stirringagitation.

A steel panel measuring 2 cm by 5 cm was prepared by an immersion in ahot (180 degrees Fahrenheit) alkaline cleaning solution for 10 minutes,rinse in water, immersion in a fifty percent by volume concentration ofhydrochloric acid in water at 70 degrees Fahrenheit for 1 minute, rinsein water, and then immersion in the plating bath of the presentinvention at the parameters disclosed above. After 120 minutes ofplating in this plating bath the panel was removed from the platingbath. The coating on the panel was analyzed as follows.

A photograph of a cross section of this coating at 1000-× magnificationdemonstrated a coating thickness of 45-50 microns, i.e.: 22.5-25 micronsper hour, which is somewhat faster than the standard plating rate. Thephotomicrograph also demonstrated a uniform dispersion of particleswithin the metal alloy matrix.

EXAMPLE 6

Nickel-Boron Carbide without Heavy Metals

A composite electroless nickel-boron carbide bath was formulated. Thebath included nickel salt providing a nickel metal concentration of 6grams per liter in the plating bath, a reducing agent of sodiumhypophosphate at a concentration of 30 grams per liter, an aqueousdispersion of boron carbide particles and particulate matter stabilizersin a concentration of 3.5 grams of particles per liter, and othercomponents typical of electroless nickel baths, but free of any lead orother heavy metals. The plating bath was operated at the parameters ofpH 4.8-4.9, temperature of 90 degrees Celsius, and mild stirringagitation.

A steel panel measuring 2 cm by 5 cm was prepared by an immersion in ahot (180 degrees Fahrenheit) alkaline cleaning solution for 10 minutes,rinse in water, immersion in a fifty percent by volume concentration ofhydrochloric acid in water at 70 degrees Fahrenheit for 1 minute, rinsein water, and then immersion in the plating bath of the presentinvention at the parameters disclosed above. After 120 minutes ofplating in this plating bath the panel was removed from the platingbath. The coating on the panel was analyzed as follows.

A photograph of a cross section of this coating at 1000-× magnificationdemonstrated a coating thickness of 50-60 microns, i.e.: 25-30 micronsper hour, which is somewhat faster than a standard plating rate of theprior art. The photomicrograph also demonstrated a uniform dispersion ofparticles within the metal alloy matrix.

EXAMPLE 7

Nickel-Tungsten Carbide without Heavy Metals

A composite electroless nickel-tungsten carbide bath was formulated. Thebath included nickel salt providing a nickel metal concentration of 6grams per liter in the plating bath, a reducing agent of sodiumhypophosphate at a concentration of 30 grams per liter, an aqueousdispersion of tungsten carbide particles and particulate matterstabilizers in a concentration of 3.5 grams per liter, and othercomponents typical of electroless nickel baths, but free of any lead orother heavy metals. The plating bath was operated at the parameters ofpH 4.8-4.9, temperature of 90 degrees Celsius, and mild stirringagitation.

A steel panel measuring 2 cm by 5 cm was prepared by an immersion in ahot (180 degrees Fahrenheit) alkaline cleaning solution for 10 minutes,rinse in water, immersion in a fifty percent by volume concentration ofhydrochloric acid in water at 70 degrees Fahrenheit for 1 minute, rinsein water, and then immersion in the plating bath of the presentinvention at the parameters disclosed above. After 90 minutes of platingin this plating bath the panel was removed from the plating bath. Thecoating on the panel was analyzed as follows.

A photograph of a cross section of this coating at 1000-× magnificationdemonstrated a coating thickness of 100 microns, i.e.: 66 microns perhour, which is fast compared to the standard plating rate. Thephotomicrograph also demonstrated a uniform dispersion of particleswithin the metal alloy matrix.

EXAMPLE 8

Nickel-Graphite Fluoride without Heavy Metals

A composite electroless nickel-graphite fluoride bath was formulated.The bath included nickel salt providing a nickel metal concentration of6 grams per liter in the plating bath, a reducing agent of sodiumhypophosphate at a concentration of 30 grams per liter, an aqueousdispersion of graphite fluoride particles and particulate matterstabilizers in a concentration of 3.5 grams of particles per liter, andother components typical of electroless nickel baths, but free of anylead or other heavy metals. The plating bath was operated at theparameters of pH 4.8-4.9, temperature of 90 degrees Celsius, and mildstirring agitation.

A steel panel measuring 2 cm by 5 cm was prepared by an immersion in ahot (180 degrees Fahrenheit) alkaline cleaning solution for 10 minutes,rinse in water, immersion in a fifty percent by volume concentration ofhydrochloric acid in water at 70 degrees Fahrenheit for 1 minute, rinsein water, and then immersion in the plating bath of the presentinvention at the parameters disclosed above. After 60 minutes of platingin this plating bath the panel was removed from the plating bath. Thecoating on the panel was analyzed as follows.

A photograph of a cross section of this coating at 1000-× magnificationdemonstrated a coating thickness of 25-30 microns, i.e.: 12.5-15 micronsper hour, which is equivalent to the standard plating rate. Thephotomicrograph also demonstrated a uniform dispersion of particleswithin the metal alloy matrix.

EXAMPLE 9

Cobalt/Boron-Diamond without Heavy Metals

A composite electroless cobalt/boron-diamond bath was formulated. Thebath included cobalt salt providing a cobalt metal concentration of 7.5grams per liter in the plating bath, a reducing agent of DMAB at aconcentration of 2.5 grams per liter, an aqueous dispersion of diamondparticles and particulate matter stabilizers in a concentration of 3.5grams of particles per liter, and other components typical ofelectroless baths, but free of any lead or other heavy metals. Theplating bath was operated at the parameters of pH 6.0-6.3, temperatureof 55 degrees Celsius, and mild stirring agitation.

A steel panel measuring 2 cm by 5 cm was prepared by an immersion in ahot (180 degrees Fahrenheit) alkaline cleaning solution for 10 minutes,rinse in water, immersion in a fifty percent by volume concentration ofhydrochloric acid in water at 70 degrees Fahrenheit for 1 minute, rinsein water, and then immersion in the plating bath of the presentinvention at the parameters disclosed above. After 240 minutes ofplating in this plating bath the panel was removed from the platingbath. The coating on the panel was analyzed as follows.

A photograph of a cross section of this coating at 1000-× magnificationdemonstrated a coating thickness of about 20 microns, i.e.: about 4-5microns per hour, which is equivalent to the standard plating rate. Thephotomicrograph also demonstrated a uniform dispersion of particleswithin the metal alloy matrix.

EXAMPLE 10

Cobalt/Phosphorous-Diamond without Heavy Metals

A composite electroless cobalt/phosphorous-diamond bath was formulated.The bath included cobalt salt providing a cobalt metal concentration of7.5 grams per liter in the plating bath, a reducing agent of sodiumhypophosphite at a concentration of 25 grams per liter, an aqueousdispersion of diamond particles and particulate matter stabilizers in aconcentration of 3.5 grams of particles per liter, and other componentstypical of electroless baths, but free of any lead or other heavymetals. The plating bath was operated at the parameters of pH 9.5-10,temperature of 90 degrees Celsius, and mild stirring agitation.

A steel panel measuring 2 cm by 5 cm was prepared by an immersion in ahot (180 degrees Fahrenheit) alkaline cleaning solution for 10 minutes,rinse in water, immersion in a fifty percent by volume concentration ofhydrochloric acid in water at 70 degrees Fahrenheit for 1 minute, rinsein water, and then immersion in the plating bath of the presentinvention at the parameters disclosed above. After 180 minutes ofplating in this plating bath the panel was removed from the platingbath. The coating on the panel was analyzed as follows.

A photograph of a cross section of this coating at 1000-× magnificationdemonstrated a coating thickness of about 21 microns, i.e.: about 7microns per hour, which is equivalent to a standard plating rate. Thephotomicrograph also demonstrated a uniform dispersion of particleswithin the metal alloy matrix.

Although the invention herein has been described with reference toparticular embodiments, it is to be understood that these embodimentsare merely illustrative of the principles and applications of thepresent invention. It is therefore to be understood that numerousmodifications may be made to the illustrative embodiments and that otherarrangements may be devised without departing from the spirit and scopeof the present invention as defined by the appended claims.

1. A process for electrolessly metallizing an article to provide on thesurface thereof a metal coating incorporating therein particulatematter, said process comprising contacting the surface of said articlewith an electroless metallizing bath containing particulate matter;wherein said electroless metallizing bath is essentially free of heavymetals.
 2. The process of claim 1, wherein said electroless metallizingbath includes an aqueous solution of a metal salt, a reducing agent, anda particulate matter stabilizer;
 3. The process of claim 1, wherein saidmetal coating comprises one or more metals or one or more metals andphosphorous.
 4. The process of claim 3, wherein said metal is selectedfrom a group consisting of nickel, cobalt, boron, and copper
 5. Theprocess of claim 4, wherein said metal coating is selected from a groupconsisting of nickel, a nickel-phosphorous alloy, a nickel-boron alloy,cobalt, a cobalt-phosphorous alloy, a cobalt-boron alloy, and copper. 6.The process of claim 1, wherein said particulate matter is selected froma group consisting of polytetrafluoroethylene (PTFE), diamond, siliconcarbide, boron nitride (BN), aluminum oxide, graphite fluoride, tungstencarbide, talc, molybdenum disulfide (MoS), boron carbide and graphite.7. The process of claim 1, wherein said particulate matter comprisesparticles having wear-resistant properties.
 8. The process of claim 7,wherein said particles are selected from a group consisting of diamond,carbides, oxides and ceramics.
 9. The process of claim 1, wherein saidparticulate matter having lubricating properties.
 10. The process ofclaim 9, wherein said particles are selected from a group consisting ofpolytetrafluoroethylene (PTFE), boron nitride (BN), talc, molybdenumdisulfide (MoS), graphite, and graphite fluoride.
 11. The process ofclaim 1, wherein said electroless metallizing bath contains a heavymetal concentration of no more than 0.045 ppm.
 12. The process of claim11, wherein said electroless metallizing bath contains a heavy metalconcentration of no more than 0.030 ppm.
 13. An electroless metallizingbath comprising an aqueous solution of metal salt, a reducing agent,particulate matter, and a particulate matter stabilizer; wherein saidelectroless metallizing bath is essentially free of heavy metals. 14.The electroless metallizing bath of claim 13, wherein said metal saltcomprises a metal selected from a group consisting of nickel, cobalt andcopper.
 15. The electroless metallizing bath of claim 13, wherein saidparticulate matter is selected from a group consisting ofpolytetrafluoroethylene (PTFE), diamond, silicon carbide, boron nitride(BN), aluminum oxide, graphite fluoride, tungsten carbide, talc,molybdenum disulfide (MoS), boron carbide and graphite.
 16. Theelectroless metallizing bath of claim 13, wherein said particulatematter comprises particles having wear-resistant properties.
 17. Theelectroless metallizing bath of claim 16, wherein said particles areselected from a group consisting of diamond, carbides, oxides andceramics.
 18. The electroless metallizing bath of claim 13, wherein saidparticulate matter comprises particles having lubricating properties.19. The electroless metallizing bath of claim 18, wherein said particlesare selected from a group consisting of polytetrafluoroethylene (PTFE),boron nitride (BN), talc, molybdenum disulfide (MoS), graphite andgraphite fluoride.
 20. The electroless metallizing bath of claim 13which contains a heavy metal concentration of no more than 0.045 ppm.21. The electroless metallizing bath of claim 20 which contains a heavymetal concentration of no more than 0.030 ppm.
 22. An article with acoating thereon, said coating comprising a metal or metal alloy andparticulate matter, wherein said coating is essentially free of heavymetals.
 23. The article of claim 22, wherein said metal or said metalalloy is selected from a group consisting of nickel, boron, cobalt andcopper.
 24. The article of claim 22, wherein said metal alloy furthercomprises one or more said metals or one or more said metals andphosphorous.
 25. The article of claim 24, wherein said metal alloy isselected from a group consisting of a nickel-phosphorous alloy,nickel-boron alloy cobalt-boron, and cobalt-phosphorous alloy.
 26. Thearticle of claim 22, wherein said particulate matter is selected from agroup consisting of polytetrafluoroethylene (PTFE), diamond, siliconcarbide, boron nitride (BN), aluminum oxide, graphite fluoride, tungstencarbide, talc, molybdenum disulfide (MoS), boron carbide and graphite.27. The article of claim 22, wherein said particulate matter comprisesparticles having wear-resistant properties.
 28. The article of claim 27,wherein said particles are selected from a group consisting of diamond,carbides, oxides and ceramics.
 29. The article of claim 22, wherein saidparticulate matter comprises particles having lubricating properties.30. The article of claim 29, wherein said are selected from a groupconsisting of polytetrafluoroethylene (PTFE), boron nitride (BN), talc,molybdenum disulfide (MoS), graphite, and graphite fluoride.
 31. Thearticle of claim 22 which contains a heavy metal concentration of nomore than 0.1% by weight of said coating.
 32. The article of claim 31which contains a heavy metal concentration of no more than 0.01% byweight of said coating.